The invention relates to an auxiliary data transmission device for a circuit breaker, said device comprising processing means comprising:                a first input to receive, in at least one configuration, a first data item representative of a state of said circuit breaker, and        at least one command output to command transmission of a data item.        
The invention also relates to an auxiliary unit of an electrical circuit breaker comprising the auxiliary data transmission device.
The invention also relates to a circuit breaker comprising said auxiliary unit.
The invention finally relates to a data transmission method for a circuit breaker comprising:                a read step, in at least one configuration, of a first data item representative of a state (O,C) of said circuit breaker, and        a command step to command data transmission.        